Initially, on susceptible poplars, small, yellow spots appear on the upper leaf surface. On the lower leaf surface, pale yellow to orange powdery uredia (which contain the tiny spores that can reinfect poplar) will be present As the season progresses, the diseased leaves turn to a crust-like orange-brown appearance which is the overwintering stage of the rust, that permits survival on fallen leaves. The fungus has a secondary host on larch/tamarack (Larix laricina). In areas where the disease is a common occurrence, the disease severity on the poplar leaves may produce disfigured leaves triggering leaves to fall from the tree. The more susceptible a tree is to leaf rust, the sooner the loss of leaves begins. Spores produced in spring from these overwintering stages on fallen leaves can infect nearby larch trees in the early spring, if present. Later in the season, spores produced on infected larch branches reinfect poplars.